Tuning means comprising variable condenser and adjustable inductor of the mechanicaly deformable type



1949- w. o. BRADFORD ETAL 93 TUNING MEANS COMPRISING VARIABLE CONDENSERAND ADJUSTABLE INDUCTOR OF THE MECHNICALLY DEFORMABLE TYPE Filed Sept.26, 1945 Patented Jan. 18, 1949 TUNING MEANS COMPRISING VARIABLECONDENSER AND ADJUSTABLE INDUCTOR F THE MECHANICALLY DEFORMABLE TYPEWilliam 0. Bradford and Emil G. Zapor, Baltimore, Md., assignors toBendix Aviation Corporation, South Bend, 1nd,, a corporation of DelawareApplication September 26, 1945, Serial No. 618,748

4 Claims. 1

This invention relates to tuning means employing adjustable inductorsand more particularly to tuning means of this type employed inconnection with high frequency receivers. The desired variation incharacteristic is secured by alteration of the mechanical dimensions ofthe inductor structure.

To secure the performance required in present day radio communicationapparatus, it is necessary that the various circuits be accurately tunedwith respect to the incoming signal frequency and, in superheterodynereceivers, it is further necessary that the resonant frequency of theoscillator circuits maintain a. special relationship to the resonancefrequency of the signal responsive circuits, the two frequencies usuallydiffering by an amount equal to the intermediate frequency of thereceiver. To this end, it is customary to employ in the oscillatorcircuit a coil having inductance different from the coils present in thesignal frequency circuit. Since the commonly available gang capacitorshave identical individual sections, the necessary difference in tuningratio is made up by a padding capacitor connected to the capacitorsection controlling the oscillator circuit.

In the alignment of such receivers, it is desirable to control theminium oscillator frequency as Well as the tuning ratio of the circuit,and for this reason some means is usually provided for varying theinductance of the oscillator coil. At frequencies below two megacyclesper second an adjustable iron core is frequently employed, whoseposition within the coil is adjusted to provide the desired inductance.At higher frequencies up to thirty megacycles per second, it becomesmore difiicult to provide iron whose magnetic properties aresatisfactory and there are, therefore, employed devices relying onmagnetic fields produced by eddy currents to adjust the coil inductors.A typical example is the use of a brass plunger movable along the axisof the coil. Insertion of the plunger in the coil reduces the inductancethereof because of the eddy current reaction on the magnetic field. Inthis case, it is evident that power losses are reflected into the coil.

When working with signals of the order of 100 megacycles persecond, itbecomes quite difficult to prdouce iron having high enough permeabilityto permit adequate control of the inductance which, at the same time,has low losses, and the use of the eddy current method in itself reliesupon the existence of losses for the control of inductance. Circuitimpedances, as controlled by stray capacitors at megacycles per second,are unfavorable to the efficient operation of Vacuum tube amplifiers,and reduction in the operating Q of the circuit due to losses introducedby inductance controlling means greatly aggravate these difficulties.

To escape the disadvantages occurring from the use of conducting or highpermeability adjustable coil cores, employment of air coils has beenmade. For the performance of the alignment or tracking operation, theoperator mechanically deforms the coil, changing its effective length orturn spacing to control the inductance. The residual elasticity of thecoil inductors makes it impossible to adjust directly to the desiredvalue because of its tendency to return to the original shape. Toovercome this, the operator is forced to distort the coil beyond thefinal desired configuration and trust that he has estimated theelasticity correctly enough to result in the required ultimateadjustment. This adjustment by successive approximation istime-consuming and requires a skilled operator.

One of the principal objects of the invention is the provision of a newand novel tuning means utilizin a conveniently adjustable inductor whoselosses are not substantially greater than that of the coil structureitself.

Another object of the invention is the provision of a new and noveltuning means including an inductor, the latter being adjustable byaction of a control means which employs neither magnetic nor conductivematerial in the field of the coil.

A further object of the invention is the provision of a new and noveltuning means utilizing an adjustable inductor of the mechanicallydeformable type which may be directly adjusted to its final desiredvalue.

The above objects and advantages of the invention are substantiallyaccomplished by the use of a tuning arrangement in which one end of adeformable coil is anchored to a fixed surface and conductivelyconnected to the stator of a rotary condenser while the other end issecured to a pivoted arm which may be swung about its pivot by theaction of an eccentric adjusting screw, and secured in its finalposition by a cooperating locking screw, the arm conductively c0nnectingthe coil to the condenser rotor.

Other objects and advantages of the invention will in part be disclosedand in part be obvious when the following specification is read inconjunction with the drawings in which:

Figure 1 is a front view of the coil and the adjusting mechanism;

Figure 2 is a side view of a condenser assembly showing the adjustingmechanism,

Referring now to Figures 1 and 2, there is shown an air core coil '10with a fixed number of turns determined by the intended frequency rangeof operation. One end I? of coil is electrically connected to the statorsection M of the associated gang condenser, and secured mechanically bya phenolic high frequency insulator strip l6, riveted to the metallicend plate l8 of the frame of the gang condenser. The end of the coil isattached, as by soldering, to one end of the arm 22, having its otherend pivotally connected to the end plate 58 by the rivet 24. The arm 22is fabricated of conductive material and serves as a ground link betweenthe end 20 of coil ID, and the end plate 18. The condenser rotor 11 andthe end plate 18 are electrically connected by virtue of the fact thatthe rotor plates are di-. rectly mounted on the condenser control shaftl9 which is journaled in the end plate 18. Hence, the coil H3 iseifectively connected directly across the electrodes of the variablecapacitor assembly and may be tuned to resonance with any desiredfrequency thereby. The arm 22 is provided with an elongated slot 28extending longitudinally thereof. An eccentric adjusting means 30 ismounted on the end plate 58. It comprises a circular head 3|, providedwith a screwdriver slot, and a shaft portion 33 having one end securedto the underside of the head 3i in an eccentric location. The adjustingmeans is mounted with the head disposed within the slot 26 and the shaftextending through the end plate IS, the free end being riveted. Theadjusting means makes a friction fit with the end plate l8 and the arm22, thus being rotatable by means of a screwdriver or similar tool forthe adjustment of the length of the coil it. A locking screw 28 passesthrough an arcuate slot 32 formed in the arm 22, the arc of the slotbeing concentric With the rivet 24, and extends into a tapped aperturein the end plate i8.

When it is desired to adjust the inductance of coil I, the locking screw28 is loosened and the eccentric adjuster 3i! rotated using a screwdriver or other suitable tool, thus rocking the arm 22 about the pivot24. The movement of the free end of arm 22 now extends or compresses thecoil 10 to the extent necessary to adjust the inductance to therequisite value. The locking screw 28 may now be tightened topermanently secure the assembly in this position.

The described mechanism provides for easy, quick, accurate and permanentadjustment of the inductance, and the connection of the adjustingmechanism to the ground side of the coil prevents energy losses.

It will be obvious that many changes and modifications may be made inthe invention without departing from the spirit thereof as described inthe foregoing description and in the appended claims.

What is claimed is:

1. In combination with a variable capacitor having a conductive endplate electrically connected to a rotor insulated from a stator, aninductive winding, electric insulating means me,- chanically securingone end of said inductive winding to said end plate, means electricallyconnecting said one end of said winding to said stator, and electricallyconductive means carried by and electrically engaging said end plate,said conducting means being secured to the remaining end of saidinductive winding and movable with respect to said end plate to vary thelength of said winding.

2. In combination with a variable capacitor having a conductive endplate electrically connected to a rotor insulated from a stator, aninductive Winding, electric insulating means mechanically securing oneend of said inductive winding to said end plate, means electricallyconnecting said one end of said winding to said stator, an electricallyconductive means carried by and electrically engaging said end plate,said conductive means being secured to the remaining end of saidinductive winding, means adjustable to move said conductive means withrespect to said end plate to vary the length of said winding, and meansoperable to lock said conductive means with respect to said end plate.

3. In combination with a variable capacitor having a conductive endplate electrically connected to a rotor insulated from a stator, aninductive winding, electric insulating means mechanically securing oneend of said inductive winding to said end plate, means electricallyconnecting said one end of said winding to said stator, a conductive armpivotally and conductively secured near one end to said end plate andconductively secured near its other end to the remaining end of saidwinding, said conductive arm being provided with a slot extendingsubstantially radially from said pivot point, and rotatable eccentricadjusting means secured to said end plate and engaging said slot.

4. In combination with a variable capacitor having a conductive endplate electrically connected to a rotor insulated from a stator, aninductive winding, electric insulating means mechanically securing oneend of said inductive winding to said end plate, means electricallyconnecting said one end of said Winding to said stator, a conductive armpivotally and conductively secured to said end plate, said arm beingconductively secured to the remaining end of said winding and beingprovided with a first slot extending substantially radially from saidpivotal point and a second slot disposed substantially perpendicularlyof said first slot, rotatable eccentric adjusting means secured to saidend plate and engaging said first slot, and a locking member passingthrough said second slot and thread edly engaging said end plate.

WILLIAM O. BRADFORD. EMIL G. ZAPOR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 793.77.? Fessenden July 4, 19051,533,749 Meirowsky Apr. 14, 1925 1,552,266 Bradley Sept. 1, 19251,913,978 Ewen June 13, 1933 2,106,120 Lindberg Jan. 18, 1938 2,367,576Harvey et al. a Jan. 16, 1945 FOREIGN PATENTS Number Country Date542,395 Great Britain Jan. 7, 1942

